Abstract Project 1 In the previous funding period, we demonstrated that validated measures of perceived stress and self-reported pain, based on 4 week recall, predict faster cognitive decline, as well as an increased incidence of amnestic mild cognitive impairment (aMCI) and dementia. We propose to improve the measurement of stress and pain, through the use of repeated ambulatory home-based assessments using smartphones. The overarching purpose of this project is to clarify the relationships, as well as the psychological and biological correlates, linking stress and pain to cognitive status and decline, using innovative ambulatory measures. From a systematically-recruited sample of Bronx residents (ages 60+), we will enroll 420 participants into our ambulatory measurement study. Using an ecological momentary assessment (EMA) design, participants will report on stress and pain each morning and night and at 5 additional times daily. At these times, Project 3 will assess subjective cognition based on self-report, and objective cognition based on 3 brief tests of memory, executive functioning and processing speed. This project will measure psychological factors including unconstructive repetitive thoughts (URTs) and pain catastrophizing, as well as biological measures including salivary cortisol and hair cortisol, which link stress and pain to cognitive outcomes. . The project has 3 specific aims: Aim 1. To assess the long-term influence of stress and pain on cognitive decline and incident aMCI using intensive ambulatory measurements. Aim 2. To assess the short- term effects of stress and pain on day-to-day variation in cognitive performance Aim 3. To examine the links among stress, pain, neuroimaging and cognition. These aims include hypotheses about psychological and biological factors. The significance of this project lies in the long-term opportunity to prevent dementia by remediating stress and pain. The innovation arises from our use of novel ambulatory methods to measure stress and pain and link it to ambulatory cognitive measures (from Project 3). We seek to identify predictors of vulnerability to stress and pain as candidate targets for intervention. The impact of this research will inform the design of clinical trials through better detection of individuals vulnerable to stress and pain that will guide the development of interventions and through enhanced measurement of cognitive outcomes.